Subsea well head pressures have been measured and surface indication provided at the surface electrically and pneumatically but difficulty has been encountered in utilizing hydraulics therefor.
The use of an electric signal to the surface to provide an indication of pressure is disclosed in the Bruce et al. U.S. Pat. No. 3,815,673. A pneumatic system for determining static pressure in a well bore is suggested by the Bell et al. U.S. Pat. No. 2,792,709. The Luke U.S. Pat. No. 3,729,997 uses a gas bubbling device to determine liquid level and includes a sensor with two diaphragm chambers, the diaphragms being interconnected by a lever type of mechanism to provide a comparison of pressures and to introduce bubbles to neutralize the diaphragm forces. There is no attempt to compensate for hydraulic head. Also, fluid relays having multiple diaphragm compartments have been used to compare or otherwise interrelate at least two fluid pressures in a control system. An example of such fluid relays is offered by Moore Products Co. of Spring House, Pennsylvania as multifunction computing relays.